From the wiki:
"I'm uploading a model to my SD card — why is this taking so long?"
The data transfer speed to your bot's SD card is infernally slow. This is why most of us at the BotCave will go ahead and eject the SD card from the bot and copy the .s3g files for printing directly from a computer. How you do this is to generate the G-code for your print, double-check that the z-height maximum in the Homing section of the G-code is correct, and then click the button "Build to File."

The resulting .s3g file can be dragged from wherever you have saved it directly to your SD card attached to your computer. Then eject the SD card, re-insert it into your bot, and use the ReplicatorG command "Build from SD card" to print your item.

It might help to create an S3G folder on your computer so that you can quickly load your favorite models to your SD card for using the "Build from SD Card" button or selecting with your Gen4 Interface Board Kit.